The present invention is related to a wireless receiver, a wireless receiving method, and a recording medium for recording thereon a program used to execute this wireless receiving method. More specifically, the present invention is directed to such a wireless receiver equipped with a stepped gain control type automatic gain control circuit, or a continuous gain control type automatic gain control circuit, and also directed to such wireless receiving method/recording medium used with the wireless receiver. The stepped gain control type automatic gain control circuit changes the gain only by a predetermined amount when a signal level of a reception signal exceeds a preselected level. The continuous gain control type automatic gain control circuit changes the gain in response to a signal level of a reception signal.
In presently available wireless (radio) receivers such as pagers, while automatic gain control circuits are mounted, gains of these automatic gain control circuits are controlled, so that intermodulation sensitivity suppression (will be abbreviated as an xe2x80x9cIMxe2x80x9d hereinafter) characteristics and over-input characteristics of these wireless receivers may be improved. Presently, there are two sorts of automatic gain control circuits. That is, in a so-called xe2x80x9ccontinuous gain control typexe2x80x9d automatic gain control circuit, a gain control amount is varied in response to a signal level of a signal entered into a wireless receiver (radio receiver). In a so-termed xe2x80x9cstepped gain control typexe2x80x9d automatic gain control circuit, when a signal level of a signal entered into a wireless receiver exceeds a certain constant level, a preselected amount of gain is controlled.
First, a conventional wireless receiver equipped with a continuous gain control type automatic gain control circuit will now be explained with reference to FIG. 12 and FIG. 13. FIG. 12 is a structural diagram for showing the conventional wireless receiver equipped with the continuous gain control type automatic gain control circuit (first prior art).
In FIG. 12, the wireless receiver of the first prior art is arranged by employing an antenna 501, a low noise signal amplifier (LNA) 502, a local oscillator circuit 503, a frequency converting circuit 504, a Received Signal Strength Indicator (RSSI) 505, and a gain control circuit 506
The antenna 501 receives a signal transmitted from a base station (not shown). The low noise signal amplifier 502 amplifies the signal received by the antenna 501. The frequency converting circuit 504 performs the signal converting operation by multiplying the signal amplified by the low noise signal amplifier 502 by the signal of the local oscillator circuit 503. The Received Signal Strength Indicator (RSSI) 505 changes a voltage of an output signal GC5 in response to a signal level of an intermediate frequency signal IF after being frequency-converted. The gain control circuit 506 changes a control amount of a gain in response to the output signal GC5 outputted from the Received Signal Strength Indicator 505.
When a level of a signal entered to the antenna 501 is changed, the signal level of the intermediate frequency signal IF which is frequency-converted by the frequency converting circuit 504 is changed in response to this signal level change. Then, the voltage of the output signal GC5 of the Received Signal Strength Indicator 505 is varied in response to the level change of the signal IF which is frequency-converted by the frequency converting circuit 504, so that the gain control amount of the gain control circuit 506.
In other words, while the automatic gain control circuit is operated, when the signal level of the signal entered into the antenna 501 is high (namely, when electric field strength is strong), the gain control amount is increased, whereas when the signal level thereof is low (namely, when electric field strength is weak), the gain control amount is decreased. As previously explained, since the gain control amount will be changed in response to the signal level, the signal level of the intermediate frequency signal IF after being frequency-converted may be kept substantially constant until the gain control amount reaches the limit value and then becomes saturated. In this case, in such a case that the electric field strength changing width of the wireless signal entered into the antenna 501 while the automatic gain control circuit is operated is larger than, or equal to a difference (namely, sensitivity margin when AGC operation is active) between the sensitivity and the operation-starting electric field strength value of the automatic gain control (will be abbreviated as an xe2x80x9cAGCxe2x80x9d hereinafter) operation, and furthermore, the signal level is varied at such a pitch higher than the following speed with respect to the signal level change in the AGC operation, the electric field strength becomes lower than, or equal to the sensitivity point when the signal level is dropped. As a result, it is required to secure the sufficiently large sensitivity margin while the AGC operation is carried out.
FIG. 13 is an explanatory diagram for explaining a relationship between an operation-starting electric field strength value of an AGC operation, and both sensitivity margin when the AGC operation is performed and an IM characteristic in the continuous gain control type automatic gain control circuit.
When the operation-starting electric field strength value of the AGC operation of the automatic gain control circuit is a low level, although a calling available area (AR3) in the IM characteristic is increased, since the sensitivity margin is small when the AGC operation is performed, the AGC operation is weakened with respect to the field strength variation of the desirable electromagnetic wave. Also, when the operation-starting electric field strength value of the AGC operation of the automatic gain control circuit is a high level, although a calling available area (AR2) in the IM characteristic which can be improved by the automatic gain control circuit is decreased, since the sensitivity margin is made large when the AGC operation is performed, the AGC operation is strengthened with respect to the field strength variation of the desirable electromagnetic wave. As explained above, the operation-starting electric field value of the AGC operation must be set by considering both the IM characteristic and the sensitivity margin when the AGC operation is carried out.
Next, another conventional wireless receiver equipped with a stepped gain control type automatic gain control circuit will now be explained with reference to FIG. 14 to FIG. 16. FIG. 14 is a structural diagram for showing the conventional wireless receiver equipped with the stepped gain control type automatic gain control circuit (second prior art).
In FIG. 14, the wireless receiver of the second prior art is arranged by employing an antenna 601, a low noise signal amplifier (LNA) 602, a local oscillator circuit 603, a frequency converting circuit 604, a Received Signal Strength Indicator (RSSI) 605, and a gain control circuit 606.
When a signal level of an intermediate frequency signal IF which is frequency-converted by the frequency converting circuit 604 becomes higher than, or equal to a predetermined value, the Received Signal Strength Indicator (RSSI) 605 changes a signal GC6 to output the changed signal. The operation condition (ON-condition/OFF-condition) of the gain control circuit 606 is switched in response to the signal GC6 derived from the Received Signal Strength Indicator 605.
In this case, the gain control amount controlled by the gain control circuit 606 is made constant irrespective of a level of a signal entered from the antenna 601. Also, since a large amount of gains are instantaneously controlled within one time in the stepped gain control type automatic gain control circuit, large noise may be produced when the gain is controlled (switched). As a result, normally, both the field strength detecting operation and the gain switching operation are completed within a synchronization portion of a signal, and the gain switching operation is not carried out within a data section.
Also, in the case that an electric field variation width of a wireless signal entered into the antenna 601 is higher than, or equal to a difference (namely, sensitivity margin when AGC operation is carried out) between the operation-starting field strength value of the AGC operation and the sensitivity when the AGC operation is carried out, it is so judged that the signal level is high when the electric field strength is detected, namely high electric field. As a result, the automatic gain control circuit is caused to be operated. Since it is conceivable that the electric field strength is dropped lower than, or equal to the sensitivity point when the AGC operation is carried out in the data section and therefore the transmitted data cannot be received, the sufficient sensitivity margin when the AGC operation is carried out must be secured.
FIG. 15 is an explanatory diagram for representing a relationship among an AGC operation-starting electric field strength value, a gain control amount, and a calling rate in the stepped gain control type automatic gain control circuit. It should be understood that in this drawing, a calling rate of 80 [%] is defined as a sensitivity point.
When the gain control amount is increased so as to increase a gain-lowering amount, a sensitivity point when the AGC operation is performed is deteriorated in connection with increasing of this gain-lowering amount. For example, as shown in FIG. 15, the following two cases will now be considered in such a case that the static sensitivity of the automatic gain control circuit is turned OFF (namely, non-operation state) is equal to 20 [dBxcexcV/m], namely the gain control amount is set to 10 [dB], and is set to 15 [dB]. When the gain control amount is selected to be 10 [dB], namely small, the static sensitivity achieved while the AGC operation is performed is deteriorated by 10 [dB] to thereby become 30 [dBxcexcV/m]. When the gain control amount is selected to be 15 [dB], namely large, the static sensitivity achieved while the AGC operation is carried out is deteriorated by 15 [dB] to thereby become 35 [dBxcexcV/m].
In the case that an AGC operation-starting electric field strength value is set to 40 [dBxcexcV/m] in a static electric field, when the gain control amount is selected to be 10 [dB], the sensitivity margin achieved when the AGC operation is performed is 10 [dB], whereas when the gain control amount is selected to be 15 [dB], the sensitivity margin achieved when the AGC operation is performed is 5 [dB]. As previously explained, when the AGC operation-starting electric field strength value is the same, the larger the AGC gain control amount is made, the lower the sensitivity margin achieved when the AGC operation is performed becomes.
FIG. 16 is an explanatory diagram for representing a relationship among an AGC operation-starting electric field strength value, a gain control amount, and a calling available area in an IM characteristic in the stepped gain control type automatic gain control circuit. Considering now that the AGC operation-starting electric field strength is the same, when the gain control amount is increased, the calling available area on the IM characteristic is increased from xe2x80x9cAS2xe2x80x9d to xe2x80x9cAS3xe2x80x9d by way of the automatic gain control circuit, whereas when the gain control amount is conversely decreased, the calling available area on the IM characteristic is reduced by way of the automatic gain control circuit. As previously explained, also in this stepped gain control type automatic gain control circuit, the automatic gain control circuit must be set by considering both the sensitivity margin and the IM characteristic when the AGC operation is carried out.
However, in the above-explained conventional wireless receiver, although the reception sensitivities of the wireless receiver are different from each other under the transmission conditions (transfer speeds and number of FM levels) of the transmission signals, the automatic gain control circuits under all of such transfer speeds and all of the number of FM levels are set under the same setting conditions.
For instance, the following assumption is made in an FLEX type pager. That is to say, a sensitivity of the best sensitivity at 1,600 [bps/2-Level FM] is 16 [dBxcexcV/m]; and a sensitivity of the worst sensitivity at 6,400 [bps/4-Level FM] is 20 [dBxcexcV/m], namely there is a difference of 4 [dB] between both the sensitivities. In such a case that a wireless receiver equipped with the continuous gain control type automatic gain control circuit, when sensitivity margin while an AGC operation is performed requires 10 [dB] as minimum margin by considering a variation in electric fields, this wireless receiver must be set so as to secure 10 [dB] in the worst sensitivity at 6,400 [bps/4-Level FM].
However, since the sensitivity margin when the AGC operation is carried out owns 14 [dB] in the sensitivity at 1,600 [bps/2-Level FM], even when the AGC operation-starting electric field strength value at 1,600 [bps/2-Level FM] is set to such a lower electric field level than the AGC operation-starting electric field strength value at 6,400 [bps/4-Level FM] by 4 [dB], the sensitivity margin may be secured by 10 [dB] while the AGC operation is carried out. Since the AGC operation-starting electric field strength value is set to be further low electric field levels, the calling rate in the area on the IM characteristic can be furthermore improved.
Similar to another wireless receiver equipped with the stepped gain control type automatic gain control circuit, assuming now that the AGC operation-starting electric field strength value is 40 [dBxcexcV/m], the sensitivity at 1,600 [bps/2-Level FM] and the sensitivity at 6,400 [bps/4-Level FM] while the AGC operation is carried out are 26 [dBxcexcV/m] and 30 [dBxcexcV/m], the sensitivity margin while the AGC operation is performed as to 1,600 [bps/2-Level FM], and 6,400 [bps/4-Level FM] becomes 14 [dB] and 10 [dB], respectively.
When it is acceptable that as the sensitivity margin while the AGC operation is carried out, 10 [dB] is maintained at minimum the following possibilities may occur. That is, while the AGC operation starting electric field value is set to be lowered by 4 [dB], the calling rate in the area with respect to the IM characteristic may be furthermore improved. Also, in the case of the better sensitivity, at 1,600 [bps/2-Level FM], even when such a larger gain control amount than that for 6,400 [bps/4-Level FM] by 4 [dB] equal to the sensitivity difference is applied, the same sensitivity margin while the AGC operation is carried out can be obtained. As a consequence, there are certain possibilities that while the large gain control amount is set, the calling rate in the area on the IM characteristic can be furthermore improved.
As previously explained, the optimum setting conditions of the automatic gain control circuit will differ from each other, depending upon the transfer speed of the reception signal and the number of FM level. However, in the conventional wireless receiver, there is no means capable of individually setting the automatic gain control circuit in accordance with the respective transfer speeds and the respective number of FM levels. Thus, since the automatic gain control circuit is operated under the same setting conditions (namely operation-starting electric field strength values and gain control amount) as to all of the transfer speeds and the number of FM levels, this automatic gain control circuit cannot be continuously set under optimum conditions.
The present invention has been made to solve the above-explained problems occurred in the conventional wireless receivers, and therefore, has an object to provide a wireless receiver capable of setting an automatic gain control circuit under optimum conditions with respect to the respective transfer speeds of reception signals and the respective number of FM levels thereof by selectively switching an operation-starting electric field value and also a gain control amount of this automatic gain control circuit in response to the transfer speeds and the number of FM levels of the reception signals. Thus, the wireless receiver is capable of improving a calling rate under such an environment as a strong electric field IM which may cause a problem in the actual field. Also, the present invention has another object to provide a wireless receiving method and a recording medium, while using such a wireless receiver.
To solve the above-described problem, a wireless receiver, according to the first aspect of the present invention, is featured by comprising: gain control means for controlling a gain of the wireless receiver; received signal strength detecting means for detecting an electric field strength of a reception signal; operation-starting electric field strength value determining means for determining an operation-starting electric field strength value by which the gain control operation of the gain control means is commenced in response to a transfer speed of the reception signal and a number of FM level of the reception signal; and first control means for causing the gain control means to commence the gain control operation when an electric field strength detected by the received signal strength detecting means reaches the operation-starting electric field strength value.
In the wireless receiver, the wireless receiving method, and the recording medium according to the first aspect of the present invention, the operation-starting electric field strength value determining means (operation-starting electric field strength value determining step) of the automatic gain control circuit determines the operation-starting electric field strength value by which the gain control operation of the gain control means is commenced in response to the transfer speed of the reception signal and the number of FM level of the reception signal; and the first control means (first control step) causes the gain control means to commence the gain control operation when the electric field strength detected by the received signal strength detecting means reaches the operation-starting field strength value.
More specifically, in the wireless receiver of the first aspect of the present invention, while the gain control means is constructed of the stepped gain control type gain control means, when the electric field strength reaches the operation-starting electric field strength value, the gain is changed only by a predetermined amount if the signal level of the reception signal exceeds a preselected level. Also, in the wireless receiver according to the first aspect of the present invention, while the gain control means is constructed of the continuous gain control type gain control means, when the electric field strength reaches the operation-starting electric field value, the gain is changed in response to the signal level of the reception signal.
For instance, in the case of an FLEX protocol pager, 4 different combinations may be conducted as a combination between a transfer speed and a number of FM level, namely 1,600 [bps/2-level FM], 3,200 [bps/2-level FM], 3,200 [bps/4-level FM], and also 6,400 [bps/4-level FM]. Since the information for discriminating these items is contained in the synchronization data and is received, the CPU decodes this information to determine the operation-starting electric field strength of the gain control means in response to the transfer speed of the reception signal and the number of FM level thereof. As a consequence, the operation-starting electric field strength value of the gain control means can be set under optimum condition, depending upon the sort of reception signal. It is possible to provide the FLEX protocol pager capable of furthermore improving the calling rate under such an environment as the strong electric field IM which causes the problem in the actual field.
Also, in the wireless receiver according to the first aspect of the present invention, the comparing means of the first control means compares the received signal strength detected by the electric field strength detecting means with a preselected reference value, and the preselected reference voltage of the comparing means is selectively set in response to the transfer speed of the reception signal and the number of FM level thereof. In this case, the reference voltage of the comparing means can be selectively set in response to the transfer speed of the reception signal and the number of FM level thereof.
As previously described, since the reference voltage of the comparing means is selectively set, the operation-starting electric field value of the gain control means can be set in correspondence with the transfer speed of the reception signal and the number of FM level thereof. As a result, the automatic gain control operation-starting electric field strength value can be set under optimum condition, depending upon the sort of signal.
Also, in the wireless receiver according to the first aspect of the present invention, the variable gain amplifier of the first control means amplifies the reception signal by a predetermined gain to supply the amplified reception signal to the received signal strength detecting means.
In this case, the predetermined gain of this variable gain amplifier is selectively set in response to the transfer speed of the reception signal and the number of FM level thereof.
As explained above, since a predetermined gain of the variable gain amplifier is selectively set, the operation-starting electric field value of the gain control means can be shifted in correspondence with the transfer speed of the reception signal and the number of FM level thereof. As a result, the automatic gain control operation-starting electric field strength value can be set under optimum condition, depending upon the sort of signal.
Also, in the wireless receiver according to the first aspect of the present invention, the converting means of the first control means converts the output of the received signal strength detecting means into the voltage level at a predetermined rate. In this case, the predetermined rate of the converting means is selectively set in response to the transfer speed of the reception signal and the number of FM level thereof. For example, when the received signal strength detecting means is a current output, the converting means corresponds to a current-to-voltage converting means.
As previously explained, since the predetermined rate of the converting means is selectively set, the operation-starting electric field value of the gain control means can be shifted in correspondence with the transfer speed of the reception signal and the number of FM level thereof. As a result, the automatic gain control operation-starting electric field strength value can be set under optimum condition, depending upon the sort of signal.
Also, a wireless receiver, according to the second aspect of the present invention, is featured by comprising: gain control means for controlling a gain of the wireless receiver; gain control amount determining means for determining a gain control amount of the gain control means in response to a transfer speed of a reception signal and a number of FM level of the reception signal; and second control means for changing the gain of the gain control means in response to the gain control amount.
Also, in the wireless receiver, the wireless receiving method, and the recording medium according to the second aspect of the present invention, gain control amount determining means (gain control amount determining step) for determines the gain control amount of the gain control means in response to the transfer speed of the reception signal and the number of FM level of the reception signal, and the second control means (second control step) changes the gain of the gain control means in response to the gain control amount. More specifically, in the wireless receiver according to the second aspect of the present invention, the gain control means is the stepped gain control type gain control means for changing the gain only by the predetermined gain amount when the signal level of the reception signal exceeds a predetermined level.
As previously explained, since the gain control amount of the gain control means is determined in response to the transfer speed and the number of FM level, the gain control amount can be set under optimum condition, depending upon the sort of reception signal. It is possible to provide the wireless receiver, the wireless receiving method, and the recording medium, capable of furthermore improving the calling rate under such an environment as the strong electric field IM which causes the problem in the actual field.
Also, in the wireless receiver according to the second aspect of the present invention, the distributing means of the gain control means distributes the reception signal received from the antenna to both the signal amplifying means and another signal path, and second control means changes the distribution ratio of the reception signal with respect to the signal amplifying the reception signal with respect to the signal amplifying means in the distributing means in response to the transfer speed of the reception signal and the number of FM level thereof.
In this case, the term xe2x80x9canother signal pathxe2x80x9d implies, for example, a path defined from the antenna to the ground. The distribution ratio of the reception signal flowing through this path is varied, depending upon the transfer speed of the reception signal and the number of FM level thereof. As a result, since the gain control amount can be selected, the gain control amount of the automatic gain control operation can be set under optimum condition, depending upon the sort of signal.
Also, in the wireless receiver according to the second aspect of the present invention, the output voltage of the output voltage switching circuit can be selectively set with respect to the signal amplifying means whose gain is controlled by this output voltage switching circuit, so that the gain of the reception signal is controlled. The second control means controls the gain of the signal amplifying means by selectively setting the output voltage of the output voltage switching circuit in response to the transfer speed of the reception signal and the number of FM level thereof.
As previously explained, the gain of the signal amplifying means can be controlled in response to the transfer speed of the reception signal and the number of FM level thereof by selectively setting the output voltage of the output voltage switching circuit. As a result, the gain control amount of the automatic gain control operation can be set under optimum condition, depending upon the sort of signal.
Also, in the wireless receiver according to the second aspect of the present invention, the reception signal is amplified by the signal amplifying means equipped with the current source having the current switching function of the gain control means, and also the second control means selectively sets the current value of the current source having the current switching function of the signal amplifying means in response to the transfer speed of the reception signal and the number of FM level thereof.
As explained above, since the current of the signal amplifying means can be controlled in accordance with the transfer speed of the reception signal and the number of FM level thereof by selectively setting the current value of the current source equipped with the current switching function employed in the signal amplifying means, the gain control amount of the gain control means can be essentially switched. As a result, the gain control amount of the automatic gain control operation can be set under optimum condition, depending upon the sort of signal.
Also, in the wireless receiver, the wireless receiving method, and the storage medium according to the present invention, storage means stores thereinto the parameter in response to the transfer speed of the reception signal and the number of FM level thereof, and this parameter may set/control the operation-starting electric field strength value, the gain control amount, the predetermined reference voltage of the comparing means, the predetermined gain of the variable gain amplifier, the preselected rate of the converting means, the distribution ratio of the distributing means to the signal amplifying means, the output voltage of the gain controlling output voltage switching circuit of the signal amplifying means, or the current value selection of the current source having the current switching function of the signal amplifying means.
While the control parameter produced in response to the transfer speed of the received signal and the number of FM level thereof is saved in the storage means, the operation-starting electric field strength value is set based on this control parameter. In this case, as the control parameter for setting the operation-starting electric field strength value, when the wireless receiver is arranged by the below-mentioned comparing means, this control parameter selectively sets a predetermined reference voltage of this comparing means. That is, in this wireless receiver, for instance, the comparing means compares the detected electric field strength with the reference voltage, and when the detected electric field strength reaches this reference voltage, the gain control operation of the gain control means is commenced with the gain responding to the electric field strength. Also, when. the wireless receiver is arranged in such a manner that the reception signal is amplified by the variable gain amplifier at a predetermined gain thereof and then the amplified reception signal is supplied to the number of received signal strength detecting means, the control parameter selectively sets the predetermined gain of the variable gain amplifier. Furthermore, when the wireless receiver is arranged in such a manner that the output of the number of received signal strength detecting means is converted into the voltage level in a preselected rate of the converting means, the control parameter selectively sets this preselected rate of the converting means.
Alternatively, the gain control amount of the gain control means is switched based upon the control parameter produced in accordance with the transfer speed and the number of FM level saved in the storage means, so that the gain control amount of the automatic gain control operation may be set. In this case, as the control parameter for setting the gain control amount, for example, when the wireless receiver is arranged in such a manner that the distributing means distributes the reception signal to both the signal amplifying means and another signal path, the control parameter selectively sets the distribution rate of the distributing means to the signal amplifying means. When the wireless receiver is arranged by such a signal amplifying means whose gain is controlled by the output voltage of the output voltage switching circuit, the control parameter selectively sets the output voltage of the output voltage switching circuit. Furthermore, when the wireless receiver is arranged by such a signal amplifying means equipped with the current source having the current switching function, the control parameter selectively sets the current value of the current source having the current switching function employed in the signal amplifying means.
As previously explained, since the control parameter is saved in the storage means, the automatic gain control operation-starting electric field strength value and the gain control amount can be set readily under optimum condition, depending upon the transfer speed and the number of FM level of reception signal. It is possible to furthermore improve the calling rage under such an environment as the strong electric field IM.
Furthermore, in the wireless receiver, the wireless receiving method, and the recording medium according to the present invention, the parameter of the storage means is individually adjusted based upon the gain characteristic of the wireless receiver, the intermodulation sensitivity suppressing characteristic thereof, or the electric field strength characteristic thereof. For instance, when the wireless receiver is shipped, the gain characteristic, the intermodulation sensitivity suppressing characteristic, and the electric field strength characteristic of this wireless receiver are individually tested. Then, when the parameter of the storage means is set based upon the fluctuations contained in these characteristics, the automatic gain control operation-starting electric field strength value and also the gain control amount can be set under optimum conditions in correspondence with the transfer speed of the reception signal and the number of FM level thereof in fit with the actual field state.